From e8c6577617bffa4402c07c7aa20e3c24f03c1c20 Mon Sep 17 00:00:00 2001
From: Benji Dial <benji6283@gmail.com>
Date: Sun, 6 Sep 2020 00:48:07 -0400
Subject: program loading, others

big kernel additions: paging, elf loading, separate kernel and user page allocation
it now properly loads and runs sd0:bin/init.elf
still need to determine which disk was booted from, and start the init on that disk
---
 src/kernel/pmap.c | 127 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 127 insertions(+)
 create mode 100644 src/kernel/pmap.c

(limited to 'src/kernel/pmap.c')

diff --git a/src/kernel/pmap.c b/src/kernel/pmap.c
new file mode 100644
index 0000000..8634303
--- /dev/null
+++ b/src/kernel/pmap.c
@@ -0,0 +1,127 @@
+#include <stdint.h>
+#include "panic.h"
+#include "pmap.h"
+
+#define PAGEMAP_START (0x00040000)
+#define PAGEMAP_END   (0x00060000)
+#define PAGE_USED(n) ((*(uint8_t *)(PAGEMAP_START + (n >> 3)) >> (n & 7)) & 1)
+#define CLEAR_PAGE(n)  *(uint8_t *)(PAGEMAP_START + (n >> 3)) &= ~(1 << (n & 7))
+#define SET_PAGE(n)    *(uint8_t *)(PAGEMAP_START + (n >> 3)) |=   1 << (n & 7)
+
+#define KBSS_START (0x04000000)
+#define USER_START (0x08000000)
+extern const void _kernel_bss_end;
+
+uint32_t kernel_pages_left;
+uint32_t user_pages_left;
+uint32_t max_kernel_pages;
+uint32_t max_user_pages;
+
+enum {
+  BMET_FREE = 1
+};
+
+enum {
+  BMEF_NON_VOLATILE = 0x02
+};
+
+struct bios_mmap_entry {
+  uint64_t base;
+  uint64_t length;
+  uint32_t type;
+  uint32_t flags;
+};
+
+void init_pagemap() {
+  for (uint32_t *i = (uint32_t *)(PAGEMAP_START + (KBSS_START >> 15)); i < (uint32_t *)PAGEMAP_END; ++i)
+    *i = 0xffffffff;
+
+  const struct bios_mmap_entry *mmap_p = (const struct bios_mmap_entry *)0x00010000;
+  const struct bios_mmap_entry *mmap_e = (const struct bios_mmap_entry *)(0x00010000 + *(uint16_t *)0x00004006);
+
+  for (; mmap_p < mmap_e; ++mmap_p) {
+    if (mmap_p->type != BMET_FREE)
+      continue;
+    if (mmap_p->base > 0xffffffff)
+      continue;
+
+    uint32_t base_page = ((mmap_p->base - 1) >> 12) + 1;
+
+    uint64_t end = mmap_p->base + mmap_p->length;
+    if (end > 0xffffffff)
+      end = 0x100000000;
+    uint32_t end_page = end >> 12;
+
+    for (uint32_t i = base_page; i < end_page; ++i)
+      CLEAR_PAGE(i);
+  }
+
+  uint32_t kernel_pages = (((uint32_t)&_kernel_bss_end - 1) >> 12) + 1;
+  for (uint32_t i = 0; i < kernel_pages; ++i)
+    SET_PAGE(i);
+
+  kernel_pages_left = 0;
+  for (uint32_t i = KBSS_START >> 12; i < USER_START >> 12; ++i)
+    if (!PAGE_USED(i))
+      ++kernel_pages_left;
+  max_kernel_pages = kernel_pages_left;
+
+  user_pages_left = 0;
+  for (uint32_t i = USER_START >> 12; i < 1048576; ++i)
+    if (!PAGE_USED(i))
+      ++user_pages_left;
+  max_user_pages = user_pages_left;
+}
+
+//very inneficient algorithm, just returns first hole big enough.
+//a smarter algorithm might pick the smallest one available,
+//and go by bytes (or dwords) instead of bits where possible.
+void *allocate_kernel_pages(uint32_t n) {
+  uint32_t run = 0;
+  
+  for (uint32_t page = KBSS_START >> 12; page < USER_START >> 12; ++page) {
+    if (PAGE_USED(page))
+      run = 0;
+    else if (++run == n) {
+      uint32_t start = page - run + 1;
+      for (uint32_t i = start; i <= page; ++i)
+        SET_PAGE(i);
+      kernel_pages_left -= n;
+      return (void *)(start << 12);
+    }
+  }
+
+  return 0;
+}
+
+//very inneficient algorithm, just returns first hole big enough.
+//a smarter algorithm might pick the smallest one available,
+//and go by bytes (or dwords) instead of bits where possible.
+void *allocate_user_pages(uint32_t n) {
+  uint32_t run = 0;
+  
+  for (uint32_t page = USER_START >> 12; page < 1048576; ++page) {
+    if (PAGE_USED(page))
+      run = 0;
+    else if (++run == n) {
+      uint32_t start = page - run + 1;
+      for (uint32_t i = start; i <= page; ++i)
+        SET_PAGE(i);
+      user_pages_left -= n;
+      return (void *)(start << 12);
+    }
+  }
+
+  return 0;
+}
+
+//in the future, change this to go by bytes or dwords instead of bits.
+void free_pages(const void *ptr, uint32_t n) {
+  uint32_t page = (uint32_t)ptr >> 12;
+  for (uint32_t i = page; i < page + n; ++i)
+    CLEAR_PAGE(i);
+  if ((uint32_t)ptr >= USER_START)
+    user_pages_left += n;
+  else
+    kernel_pages_left += n;
+}
\ No newline at end of file
-- 
cgit v1.2.3